<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .active {
            text-decoration: underline;
        }

        .text-dangr {
            font-weight: bold;
        }
    </style>
</head>

<body>
    <script src="../js/vue.js"></script>
    <div id="app">
        <div v-bind:class="{active:isActive,'text-dangr':hasError}">Hello</div>
        <div v-bind:class="classObj">Vue.js</div>
    </div>

    <script>
        let vm = new Vue({
                el: "#app",
                data: {
                    isActive: true,
                    hasError: true,
                    classObj: {
                        active: true,
                        'text-danger': true
                    }
                }
            })
    </script>
</body>

</html>